Pneumococcal disease accounts for more deaths than any other vaccine-preventable bacterial disease.1 Among the elderly, the case fatality rates for bacteremia approach 40 percent.2,3 Most cases are sporadic, and during the antibiotic era outbreaks caused by a single pneumococcal serotype have been rare, occurring mainly in institutions such as hospitals,4 military camps,5,6 shelters,7,8 jails,9 day-care centers,10,11 and nursing homes.12,13
Since 1990, drug-resistant pneumococcal strains have become increasingly common in the United States,14-18 making the selection of empirical treatment for pneumococcal infections difficult.15,18-20 Drug-resistant infections have also been associated with certain institutional settings, particularly day-care centers,21-24 hospitals,25-30 and a pediatric long-term care facility.31 Despite the continuing emergence of drug resistance, epidemics of drug-resistant pneumococcal disease have not been previously reported among adults in the United States. We investigated an outbreak of multidrug-resistant Streptococcus pneumoniae serotype 23F among unvaccinated nursing home residents in a rural Oklahoma community (population, 18,000) where antimicrobial resistance among S. pneumoniae isolates had not previously been observed. We studied factors associated with colonization and disease, assessed modes of transmission, and evaluated the effect of control measures.
On February 16, 1996, the Centers for Disease Control and Prevention received notification that three residents of a long-term care facility had been hospitalized with pneumococcal bacteremia within a five-day period; two had died of rapidly progressing illness that did not respond to intravenous cefuroxime therapy. Initial testing indicated that all isolates had an intermediate level of susceptibility to penicillin and cefotaxime (minimal inhibitory concentration, 1.0 μg per milliliter for both by the E test), were resistant to trimethoprim–sulfamethoxazole and erythromycin, and were susceptible only to vancomycin. The clinical microbiology laboratory of the community hospital had routinely screened all sterile-site S. pneumoniae isolates for antimicrobial resistance32 since January 1995, but no resistant isolates had been identified previously.
Epidemiologic Characteristics of the Outbreak
The nursing home in which the outbreak occurred is a 100-bed, single-story building with two wings. The members of the nursing staff frequently work on both wings. The 84 residents at the time of the outbreak ranged in age from 48 to 101 years (median, 85). Ninety-two percent were at least 65 years old; 81 percent were women, and 93 percent were white. There were 78 employees (median age, 41 years).
During the outbreak, 11 residents had illness that met the case definition, giving an attack rate of 13 percent. The 11 patients were similar to residents who were not ill in mean age, race, and sex. All 11 patients had lobar consolidation evident on chest radiography, and none had symptoms suggestive of meningitis. Multidrug-resistant S. pneumoniae, serotype 23F, was isolated from the blood of four patients and from the respiratory tract of three Three patients, all with bacteremia, died (case fatality rate, 27 percent). Only 3 residents (4 percent) had had pneumococcal vaccination, although 60 of the 84 residents (71 percent) had received influenzavirus vaccine during the fall of 1995. No cases were identified among the nursing staff.